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In ultrasonic welding of thermoplastics, which joint design is most suitable for semicrystalline materials?


Frequently Asked Questions

Component design - selection of correct joint design in particular - is a fundamental part of the ultrasonic welding process.

There are two main joint designs:

  • shear
  • projection

For semi-crystalline materials, such as nylon and PPS, the shear joint should be used - see Fig.1. With this joint design, one of the components is sheared inside the other, producing a weld at the interface. The smearing action which takes place during welding avoids premature solidification of the material, a problem which can occur in semi-crystalline materials when the projection joint is used. A flash trap, which is an area to contain material displaced from the weld, may be incorporated in the shear joint.

When using the shear joint, it is particularly important to ensure that the component is supported properly around the walls. The telescoping action of the shear joint tends to push the walls of the component outwards, effectively removing the interference required to produce the shearing action.

For amorphous thermoplastic materials, such as ABS or polycarbonate, the projection joint is usually the preferred joint design (see Fig.2). However, if a seal is required between the two components in either material type, the shear joint should be used.

Fig.1. Ultrasonic shear joint
Fig.1. Ultrasonic shear joint
Fig.2. Ultrasonic projection joint
Fig.2. Ultrasonic projection joint

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